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Confirming previous research, a new study reports that early onset puberty in girls is linked to overweight and obesity. This isn’t totally surprising, since obesity can alter the levels of reproductive hormones, prompting the body into premature puberty. Still, the implications are important, given that overweight and obesity in children has increased markedly in recent decades – and given the number of health problems that are linked to excess body weight across a lifetime. But while obesity is a likely culprit in the early onset of puberty, there are certainly others.

The authors of the new study followed over 1,200 girls, starting at age 6 to 8, in three metropolitan areas: the San Francisco Bay Area, Greater Cincinnati, and New York City. They monitored breast development over the next 7 years. The median age of breast development was 8.8 for African-American girls, 9.3 for Hispanic girls, 9.7 for Caucasian girls, and 9.7 for Asian girls.

But beyond ethnicity, body mass index (BMI) was an even stronger indicator of earlier onset puberty. The team found a strong correlation between higher BMI and earlier breast maturation: Overweight and obese girls developed breasts about a year earlier than normal-weight girls (age 8 vs. age 9, respectively). Earlier large-scale studies had shown the same phenomenon, but the current study found that the onset of breast development was earlier – across all girls – than had been observed before.

Of course, the researchers point out that there’s no indication of causality here. But given what we know about how obesity affects the body’s endocrine system, it’s likely that body mass would be an important factor. “The obesity epidemic appears to be a prime driver in the decrease in age at onset of breast development in contemporary girls,” wrote the authors.

Though obesity may well by one factor, there are likely others, like environmental compounds – chemicals like BPA and other plastics additives, for example. These compounds, many of which are known as endocrine-disruptors, may alter the function of the hypothalamic-pituitary-ovarian axis, which could lead to earlier puberty.

A larger concern with early puberty is that it’s been linked to a range of chronic health problems, like diabetes, high blood pressure, and heart disease. An increased risk of breast cancer has also been connected to earlier onset of menstruation.

But there are psychological issues at play as well, and Biro et al. suggest that early puberty leads to a disconnect between biology and psychology. In particular, the body may develop a certain level of maturity sooner, but psychologically and emotionally, girls may still be at their natural age. Earlier studies have found that girls who mature sooner physically may be at higher risk of low self-esteem and depression. “They are more likely to be influenced by older peers and more deviant peers,” said the authors, “and initiate intercourse, substance use, and other norm-breaking behaviors at younger ages.” As the women grow up, they continue to be at higher risk for depression, and other factors related to self-esteem.

"Just because you're developing more quickly physically doesn't mean you're maturing emotionally or socially," study author Frank Biro Cincinnati Children's Hospital Medical Center told HealthDay. The team will next look at the relationship between environmental chemicals and early development. In the meantime, the study calls out the importance of helping our kids make good decisions early on, and monitoring what they put in their bodies both chemically and nutritionally.